1871 century photo of nez perce woman and tipi
1871 photo of the Nez Perce in Montana

New York Public Library

On May 14, 1804, the expedition was officially underway. The party numbered more than 45, and their ages ranged from 17 to 35, with an average age of 27. On July 30 the Corps set up camp near what would become Fort Atkinson, and shortly after Lewis and Clark had made contact with the Oto and Missouria. On August 3 they held the first formal meeting between representatives of the U.S. Government and western tribes. Two weeks later Lewis and Clark would broker an arrangement with Little Thief (Oto chief ) and Big Horse ( Missouria chief) that the American government would provide goods and services in exchange for their ability to create peace among other tribes. The Corps continued on their journey following the negotiation of this agreement.

On August 20, 1804, Sgt. Charles Floyd died from what is believed to have been a burst appendix. He was the only member of the Corps of Discovery to die during the expedition. A large monument marks his resting place near Sioux City, Iowa.

By October, the Corps of Discovery reached the Mandan and Hidatsa villages located in present-day North Dakota. They built Fort Mandan, which is where they spent the winter of 1804/05.

There were five villages - two Mandan and three Hidatsa - with an estimated population of 4,500. These villages were central to trade along the Upper Missouri River, often hosting Cree, Cheyenne, Assiniboine, Crow, and Teton Sioux traders. The Lewis and Clark Expedition built Fort Mandan close to the Mandan village of Mitutanka, though the most important village to the Corps was Nuptadi (“Rooptahee” in the journals). Nuptadi was the home of Posecopsahe, the civil chief with whom the Corps would negotiate. Lewis and Clark spent the winter trading with tribes, establishing diplomatic ties, and trying (unsuccessfully) to orchestrate peace between the Arikaras and Mandans. The Corps traded for vegetables from these farming Indians and even went on hunts with the Mandan.

While at Fort Mandan, Lewis and Clark recruited Toussaint Charbonneau as an interpreter. Charbonneau was French-Canadian and had lived with the Hidatsa for many years. His (approximately)16 year old wife, Sacagawea, was Lemhi Shoshone and had been captured years earlier and was living with the Hidatsa. In February 1805, she gave birth to their baby boy named Jean Baptiste, who Clark nicknamed “Pomp” or “Pompy.”

In April, the Corps of Discovery resumed its journey. Twelve members of the crew were sent back to St. Louis to deliver collections of zoological, botanical, and ethnological specimens. They also carried letters, reports, dispatches, and maps. The party that continued west now numbered 33.

The Corps maneuvered its boats up the Missouri River through what is now Montana. By early June, they reached a place where two rivers met. They were able figure out which river led west based on American Indian descriptions of large waterfall - now known as Great Falls. They continued left up the Missouri River, and named the right fork the Marias River.


By August 17, they reached the Three Forks of the Missouri, which they named Jefferson, Gallatin, and Madison. After navigating up the Jefferson River they found nothing but mountains for as far as they could see. It became obvious, as they crossed the Continental Divide through Lemhi Pass, that there was no easy water route to the West Coast.

They were able to make contact with the Lemhi Shoshone - Sacagawea's tribe. Their chief, Cameahwait, confirmed what the Corps had feared - that there was no all-water route to the Pacific. would need to prepare for an overland journey. While negotiating with the Lemhi Shoshone, Sacagawea was surprised to see Cameahwait, who was her brother. After their reunion, negotiations between the Corps and the Lemhi Shoshone continued. Lewis was able to secure a number of pack horses, and they continued west. Sacagawea continued with them.

In the fall of 1805, the Corps traveled overland by walking with their pack horses, north to Lolo Pass, where they began their arduous 200-mile journey across the Bitterroot Mountains on the Lolo Trail. The five day journey took eleven, and the Corps was hit with several snow storms. Weather combined with the scarcity of game meant that the Corps were forced to eat some of their emergency rations and animals. By the time they reached the Nez Perce (Nimiipuu) on September 20 at Weippe Prairie, they were suffering from hunger, dehydration, and exhaustion. The Nez Perce fed and provided shelter for the Corps while also helping them prepare for the next leg of their journey - on water. Twisted Hair, a chief of the Nez Perce, and others helped the Corps find timber to make dug-out canoes. The Corps secured goods from the Nez Perce and, after receiving directions on where to go, left. The pack horses were left in the care of the Nez Perce.

The Corps continued down the Clearwater, Snake, and Columbia rivers. They reached the Pacific Ocean by mid-November 1805.

With the weather becoming harsh, the Corps decided to stay on the south side of the Columbia River. In December they built Fort Clatsop (near present-day Astoria, Oregon), and settled in for the winter. During this time Lewis and Clark gathered and recorded information about the country's geography and inhabitants.